Families of college-bound students will soon be able to file key financial aid forms. But it takes some legwork to make sure you're ready.

The Free Application for Federal Student Aid for the 2018-19 academic year can be filed starting Sunday. Colleges, as well as federal and state governments and other groups, use FAFSA data to determine eligibility for need-based financial aid. (Sunday is also the start day to file the CSS Profile, which is required by nearly 400 colleges and scholarship programs for their own aid programs, according to the College Board.)

FAFSA-filing rates have ticked up in recent years as families look for strategies to reduce the rising costs of college, said Rick Castellano, a spokesman for student loan company Sallie Mae.

"Those cost-saving measures include completing the FAFSA," he said.

In Sallie Mae's 2017 "How America Pays for College" report, 86 percent of families said they had filed the FAFSA, the highest rate in the survey's 10-year history. A decade ago, 74 percent said they had filed it. (For this year's survey, Sallie Mae polled 800 parents of undergraduate college students ages 18 to 24, as well as 800 undergraduate students ages 18 to 24.)

"When you submit your FAFSA documents, you want them to be as complete and accurate and thorough as possible."-Matt Chancey, certified financial planner

Experts say there's good reason to apply for financial aid as early as possible.

"I always ask clients, when does everybody go out to dinner? Friday night, because they just got paid," said certified financial planner T. Eric Reich, president of Reich Asset Management in Marmora, N.J. "Don't think that colleges won't be more generous on the front end, too."

State and college deadlines to apply for aid vary, but many distribute funds on a first-come, first-served basis. A 2015 Edvisors.com study found that students who file the FAFSA in the first three months have received more than double the grant money.

Even if you think you won't qualify for need-based aid, it's still worth filing the FAFSA, Castellano said. You'll need it to apply for federal student loans, and to be eligible for many colleges' merit-based aid.

It's also possible you're wrong about your aid eligibility. Students who don't file the FAFSA forgo an average $9,741.05 in aid for that academic year, according to a study published in Research in Higher Education earlier this year.

"You might get a nice surprise," Castellano said.

First-time FAFSA filers can expect to spend 55 minutes on the form, according to Edvisors.com, but that's doesn't include time spent in preparation. Here's how to get ready:

1) Wrap up your taxes

The 2018-19 FAFSA uses income data from your 2016 tax return — the one filed this year. If you're among those taxpayers taking full advantage of the six-month filing extension (with a deadline of Oct. 16, or Jan. 31, 2018, for recent hurricane victims), wrap up your return before turning to the FAFSA, said Matt Chancey, a certified financial planner based in Orlando, Florida. It's better to have hard numbers than estimates.

"When you submit your FAFSA documents, you want them to be as complete and accurate and thorough as possible," he said. "If your tax returns aren't all buttoned up, that's going to be hard."

2) Prime your assets

Asset values are reported at the time you file the FAFSA, and there are still a few last-minute changes you can make that could boost your student's chances at aid. One of the easiest: reducing cash balances you'd have to report by paying down debt or prepaying bills, Reich said.

"Pay it down and get rid of that cash," Reich said.

Other FAFSA prep strategies require more advance planning; consult a financial advisor and accountant before making any big changes. The right strategies can also vary by where your student is applying, Reich said — the CSS Profile factors in some assets and income differently than the FAFSA.

SShepard | E+ | Getty Images

3) Gather your paperwork

"Make sure you have all the materials you're going to need," Castellano said.

Those include Social Security numbers (for parents and the student), your family's latest financial statements, records of untaxed income (like child support) and driver's license numbers. Have your most recent tax return on hand, too, he said, although families filing the FAFSA online can import much of that information using the IRS data retrieval tool.

(The Department of Education has said the data retrieval tool — which the IRS took offline in March due to security concerns — will be available again in time for the FAFSA filing season open, with additional security precautions in place.)

The student and parent also need FSA IDs, Castellano said. First-timers can use their ID immediately after registering to "sign" an online FAFSA form, according to Department of Education. For other tasks, you may need to wait up to three days for your ID to be usable in the system.

Correction: This story was revised to correct that Sunday is the start of the filing season for FAFSA and the CSS Profile.